A system including a display device is often required to reduce power consumption. Power consumption reduction is one of the most important issues especially in portable terminals, such as smart phones, tablets and PDAs (personal digital assistants), and therefore a display device incorporated in a portable terminal (e.g. a liquid crystal display device) is strongly desired to reduce power consumption.
To achieve power consumption reduction, a system including a display device, e.g. a portable terminal, may be placed in a low power consumption operation state (e.g. a standby state) in accordance with the necessity. In this case, the display device may stop operating, or perform an operation to show a simple display screen (e.g. a display screen only showing the present time).
The inventors are, however, considering that the usability of a system, e.g. a portable terminal, is enhanced if the system is capable of displaying an image with an improved image quality to some extent in a low power consumption state. For example, the usability of a portable terminal would be largely improved if the portable terminal is capable of display a wallpaper with an improved image quality to some extent when the portable terminal is placed in the standby state.
Accordingly, there is a need for a technique for displaying an image with an improved image quality with reduced power consumption.
The following is a list of prior arts which may be related to the present invention. Japanese Patent Application Publication No. 2010-74506 A discloses image processing in which image data of a block composed of 8×8 pixels are color-reduced (or compressed) to three or four-color images.
Japanese Patent Application Publication No. H09-270923 A discloses a binarization process in which a threshold value is determined by using values of a dither matrix and input data of a pixel of interest are compared with the threshold value.
Japanese Examined Patent Application Publication No. H06-50522 B2 discloses a technique in which one of four tables are selected by using lower two bits of a first graylevel signal as an address, and a second graylevel signal is generated by adding an amendment value contained in the selected table to the upper four bits.
Japanese Patent Gazette No. 3,125,560 B2 discloses a technique for obtaining a pseudo graylevel output, the technique involving separating an x-bit input signal into upper n bits (where n is the bit width of a display device) and lower m bits (m=x−n), transforming the lower m bits into an one-bit output through pseudo graylevel processing, and sequentially adding the one-bit output to the upper n bits.
Japanese Patent Gazette No. 4,601,279 B2 discloses a technique for achieving an image display with an improved image quality by using a frame rate control as well as a dithering process.
Japanese Patent Gazette No. 4,646,549 B2 discloses a technique of displaying an image corresponding to display data, wherein selected one of first and second operations is performed, the first operation including storing upper and lower bits of first image data as the display data in a display memory, and the second operation including storing upper bits of first and second image data as the display data in the display memory.
Japanese Patent Gazette No. 5,632,691 B2 discloses a technique in which the graylevel of each color is modified by uniformly performing a bit shift on RGB data to thereby adjust the brightness.